1. Field of the Invention
The present invention relates to a field coil assembly for an electromagnetic clutch, and more particularly, to a field coil assembly for an electromagnetic clutch, wherein a thermal fuse is installed to a holder mounted to an electromagnetic coil body so that the height of the thermal fuse may be variably adjusted, thereby preventing damage in the thermal fuse which may be caused by a injection molding apparatus during an injection molding process.
2. Description of the Related Art
Generally, a field coil assembly for an electromagnetic clutch is an electric apparatus, in which when electric power is supplied, the electromagnetic induction of a wound coil in the field coil assembly causes a magnetic field to be generated and the magnetic force accordingly causes a disc of a pulley and a hub disc of a driving shaft of a compressor to be connected to each other, so that the electromagnetic clutch may cause the driving force of the pulley rotated by an engine to be transmitted to the hub disc of the driving shaft of the compressor. As such, the field coil assembly for an electromagnetic clutch serves to intermit power applied to the compressor depending on whether or not the electric power is supplied to the wound coil, so that the operation of a cooling system in an air conditioning apparatus can be controlled.
The field coil assembly for an electromagnetic clutch as described above includes a thermal fuse for causing the coil to be shorted when the clutch of the compressor is overheated.
In addition, when the compressor is locked due to any abnormal reasons, the thermal fuse is shorted by slip heat of the clutch, which would be generated before the compressor is locked, to cut off the electric power supplied to the electromagnetic coil, thereby causing the load due to the lock of the compressor not to be applied to the engine as well as preventing a driving belt of the compressor from being damaged.
Specifically, since the disc of the pulley slips with respect to the hub disc of the driving shaft when the compressor is locked, the temperature is excessively increased in such slipping portions. Considering the foregoing, the thermal fuse is installed adjacent to the disc of the pulley so that the thermal fuse is shorted due to the abnormal increase in temperature of such slipping portions.
Patent applications concerning such a conventional field coil assembly for an electromagnetic clutch have been filed in the name of the present applicant. FIGS. 1 and 2 show an example of a conventional field coil assembly for an electromagnetic clutch which has been proposed by the applicant.
As shown in FIG. 1, a field coil assembly 2 for an electromagnetic clutch includes an electromagnetic coil body 30 formed by winding an electromagnetic coil in a ring shape; a bobbin 20, which is made of a ring-shaped synthetic resin material and has one side being open, for receiving the electromagnetic coil body 30 therein to maintain the shape of the electromagnetic coil body 30; a field core 10, which has one side being open and receives the bobbin 20 through the open side in a groove 11 formed in the field core 10 to thereby protect the bobbin 20 and the electromagnetic coil body 30 in the bobbin 20 from an externally impact; and an epoxy injection molded body 40, which is injection molded into the field core 10 to fill a space between the bobbin 20 and the field core 10 and to fix the bobbin 20 and the electromagnetic coil body 30 into the field core 10.
In addition, as shown in FIG. 2, an outer surface of the electromagnetic coil body 30 provided in the field core 10 is provided with a holder 50, which is an insulating body formed of a circular-arc-typed plate corresponding to the outer surface of the electromagnetic coil body 30. The holder 50 is mounted with a thermal fuse 60 for disconnecting the electromagnetic coil body 30 when the clutch of the compressor is overheated.
The holder 50 is formed with a base 51 which is curved in a circular arc shape along the outer surface of the electromagnetic coil body 30. Mounting protrusions 52 are formed to protrude downwards along outer peripheries of both curved side edges of the base 51 so that the holder 50 can be fitted onto and coupled to the electromagnetic coil body 30. Two holes 51a are bored through one side of the base 51 so that two lead wires 31 of the electromagnetic coil body 30 are withdrawn toward both sides of an upper portion of the holder 50 through the holes 51a, respectively.
Further, protrusions 53 between which the thermal fuse 60 is inserted and seated are formed to protrude on the upper surface of the base 51 of the holder 50. Coupling protrusions 54, into which terminals 55 for allowing lead wires 61 of the thermal fuse 60 and the lead wires 31 of the electromagnetic coil body 30 to be electrically connected are fixedly inserted, are formed to protrude at both sides of the protrusions 53, respectively.
Meanwhile, the protrusions 53 protrude from the base 51 of the holder 50 in a vertical direction thereto and comprise a pair of plates which are spaced apart from each other on the base 51. Reference numeral 21 in FIG. 1 designates a connection protrusion, which is formed on the bobbin 20 and coupled for lead-out wires of the electromagnetic coil body 30 to be connected.
A process of assembling the conventional field coil assembly 2 for an electromagnetic clutch so configured will be described. First, the terminals 55 are fixedly inserted into the coupling protrusions 54 formed on the upper surface of the holder 50, and then, the mounting protrusions 52 at both the sides of the holder 50 enclose the outer surface of the electromagnetic coil body 30 which is received in the bobbin 20, so that the holder 50 is fixed to the electromagnetic coil body 30.
In such a state, the thermal fuse 60 is inserted and fixed between the protrusions 53 of the holder 50 and both the lead wires 61 of the thermal fuse 60 are press-fitted into both the terminals 55 as shown in FIG. 2 to thereby be electrically connected to the terminals 55, respectively. Further, both the lead wires 31 of the electromagnetic coil body 30 are also withdrawn through the holes 51a of the holder 50 and then press-fitted into both the terminals 55 to thereby be electrically connected to the terminals 55. As a result, the lead wires 31 of the electromagnetic coil body 30 are electrically connected to the lead wires 61 of the thermal fuse 60 through the terminals 55, respectively.
Finally, after the bobbin 20 in which the electromagnetic coil body 30 so coupled is provided is inserted into the field core 10, an epoxy resin is injected and molded into the field core 10 using an injection molding apparatus. Therefore, the electromagnetic coil body 30 and the bobbin 20 are fixed inside of the field core 10 as well as the electromagnetic coil body 30 and the field core 10 are insulated from each other.
Meanwhile, during such a molding process, the thermal fuse 60 is not completely embedded by the epoxy resin but is encapsulated so that one side thereof is exposed to the outside, whereby the accuracy of the temperature sensing function in the thermal fuse 60 can be further improved.
However, in the conventional field coil assembly 2 for an electromagnetic clutch so configured, the electromagnetic coil body 30 is formed by winding the electromagnetic coil several times. If the winding number of the electromagnetic coil or the overlapped type of the electromagnetic coil is varied, the height of the electromagnetic coil body 30 is not uniform, so that the protrusion degree of the thermal fuse 60 which is mounted to the electromagnetic coil body 30 through the holder 50 may vary.
Accordingly, if the protrusion height of the thermal fuse 60 from the electromagnetic coil body 30 is larger than a predetermined value, there is a problem in that when the epoxy injection molded body 40 is molded using an injection molding apparatus, the thermal fuse 60 may be pressed down by the injection molding apparatus to be damaged, thereby resulting in malfunction.